There are batteries as measures taken to convert chemical energy directly to electric energy. These batteries have the ability to discharge an electric charge or to charge and discharge an electric charge repeatedly with the use of electrochemical change and are therefore used as power sources of various electric or electronic devices. Also, there are capacitors as devices having the ability to charge and discharge an electric charge repeatedly and these capacitors are used as electric element parts of various electric or electronic devices.
Lithium ion batteries and lithium ion polymer batteries, which are secondary batteries having high energy efficiency, are currently used as power sources for portable telephones, personal computers and cameras. Also, a trial is made to use a fuel cell as a power source for automobiles. As to solar batteries, dye-sensitive solar batteries which are low cost and common types are being developed as crystal-type, amorphous-type or thin film-type solar batteries in the next generation.
In fuel cells, for example, a material obtained by coating the surface of a current collector made of an aluminum plate is coated with an active substance constituted of a carbon material is used as a cathode material.
In the dye-sensitive solar batteries, a material obtained by coating the surface of a thin-film substrate with a conductive material such as carbon materials is used as an electrode material.
In an electric double layer capacitor which is one of electrochemical capacitors, on the other hand, a material obtained by coating the surface of a current collector made of an aluminum foil with an active substance made of an active carbon powder is used as a polar electrode. Specifically, a binder material, a conductive agent and the like are added to and mixed with an activated carbon powder to prepare a slurry like material, which is then applied to the surface of the aluminum foil and then dried at ambient temperature and the dried material is cut into a predetermined size to manufacture a polar electrode. There is also the case where a polar electrode is manufactured by applying a mixture of an activated carbon powder, a resin and the like onto the surface of an aluminum foil under pressure and heating.
In an electrolytic capacitor, conventionally, a conductor made of an aluminum foil having a surface area enlarged by etching has been used for a cathode material. However, capacitors in which the surface of the electrode is enlarged by adhering a carbon powder onto the surface of an aluminum foil have been developed in recent years.
As a method of manufacturing an aluminum material coated with carbon which is to be used for electrode material such as batteries and capacitors, a method in which a carbon intermediate film or an intermediate film of a metal richer than aluminum is provided on an aluminum current collector and an active substance layer such as carbon is applied to the intermediate film is disclosed in Japanese Unexamined Patent Publication No. 2000-164466. Also, WO 00/07253 discloses a current collector used to fabricate a lithium secondary battery, which is increased in surface area, improved in binding strength with an active substance layer and has excellent charging/discharging characteristics by treating an aluminum material and a copper current collector used as a current collector in a lithium secondary battery as an aqueous acidic solution, aqueous basic solution or aqueous neutral solution and, in some cases, forming a conductive polymer film.
However, even if any of the above methods is used, the resulting aluminum material coated with carbon is inferior in adhesion between the active substance layer made of a carbon-containing material and the surface of an aluminum material. For this, there is the case where the active substance layer is separated from the surface of an aluminum material when a secondary battery or a capacitor is charged or discharged. As a result, there arises a problem that, for example, the charging/discharging characteristics and life of a secondary battery or a capacitor are dropped.
In order to obtain, for example, an electric double layer capacitor having a large capacity, it is necessary to increase the contact area between a polar electrode and an electrolytic solution by forming a thick active substance layer on the surface of a current collector. However, if a conventional aluminum material coated with carbon is used to constitute an electrode, this poses a problem that the active substance layer comprising carbon-containing substance is separated from the current collector made of an aluminum material when the capacitor is charged or discharged.